EZ81

[sub]

I made a comparison between few EZ81.
one JJ, two NOS tungsram, two NOS tesla, one NOS RFT.
PT secondary voltage was always 284VAC.
JJ - 336VDC
Tungsram A - 339VDC
Tungsram B - 340VDC
Tesla A - 338VDC
Tesla B - 338VDC
RFT - 333VDC

I know this is only few volts difference, probably inaudible .
I tried because i was inquisitive.

[zaphod_phil]

That's very interesting information. Thanks for doing that test and posting the results!

[sub]

Thank you Phil your kind word!
I think i will use NOS EZ81 only 1 reason > reliability

[marshman]

I don't always understand the technical aspects of these lovely boxes of noise we make, but I'm curious: Are those variations significant enough to warrant any sort of alterations to a circuit? They all test within a 7VDC 'frame', so would there be any noticeable difference to the human ear if one were to switch even the 'hottest' one for the 'coolest' one?

Since we're speculating, how much of a swing would be required to generate a noticeable difference? 5% would be a 17ish VDC drop, would a person really hear that?

[caseylutton]

It seems that output voltage of the EZ81 at idle only tells one part of the story. I would imagine they would each react differently under load. As you hit a note (or several notes), a big demand is made on the power supply. The rectifier and power tubes beg for mercy. We like the result. As the note decays, the demand for current is less and less. This is what contributes to the "sag" that we hear and talk so much about.

It would take a lot more time to test each of those tubes with 0%, 50%, 100% or more signal applied, but I'll bet the results would be very interesting.

Contemporary opinion is that NOS rectifiers will last for decades, we're not so sure about new ones. You can buy one nos for $30 or less or a new EH or JJ for less than $15. The nos will likely last more than twice as long.